Stunnel.disconnect: handle Nopid case (fix warning)
Stunnel.disconnect: handle Nopid case (fix warning)

Fixed a non-exhaustive match that had been there for years.

Signed-off-by: Thomas Sanders <c547603d2dd860735c4f0c043b1348f5c48c02f8@citrix.com>

thomassa/xen-api-libs-transitional,djs55/xen-api-libs-transitional